The original Z-1 harness was made with rigid full length poles. It was comfortable and clean but primarily made for comp pilots as it lacked almost any rock-up capability. This is the harness that Larry Tudor used when setting his world record flights. This harness is no longer available and manufacture was discontinued when WW began distributing Rotor harnesses. The Z2 harness was a line supported, semi-front entry harness, but lacked any spreader bars for lateral comfort. You had to slip it over your head to get into it, but it allowed for your legs to exit out the bottom zipper. The Z3 harness was a full front-entry harness with a standard front mounted chute. It was line supported with two fairly small spreader bars; one at the mains, and another behind your knees where the front to rear line entered the harness. It had a small internal storage container behind the pilots legs and two small side pockets. There was also an additional pocket built into the bottom of the chute container. The Z4 harness further improved on the Z3 by adding an additional spreader bar above the pilot's shoulders. The cut of the harness was changed to allow for wider bars and improved lateral comfort. The pockets were enlarged relative the Z3 and a flip-removable radio pouch was added above the chute container. The back storage was increased substantially and allowed for a dorsal expansion/humpback depending on how the rear zippers were configured. This also allowed for access to the rear storage area from either inside or outside the harness. The Z5 includes even more refinements to the cut of the harness for comfort and aerodynamics, and the wider spreader bars are made differently (using bolts rather than rivets) for increased strength and easier servicing of the harness. The side pockets are made far larger and can be collapsed down when not in use via compression straps. There is also an option for a DHV-certified side-mount chute container version. This harness is the first WW harness to have fully digitized patterns and is cut on the same sail cutting machine used to cut all the WW HG glider sails. The Z5 also features several improvements to make it easier to rock up in than any previous Z-harness. WW has maintained a database of the all the harnesses made since the Z3 so if you require specific custom sizing info on a used harness you can request it. You just need to provide a serial number which is usually on the spreader bar. If no serial is available they still may be able to track it if you determine the original dealer/customer and any color info.